1. Field of the Invention
This invention relates to the field of microwave technology. More particularly, this invention relates to a system and method for heating small samples and for lysing small samples of cells.
2. Description of Related Art
Cell lysis is the process of breaking apart the cell membrane to release the cell contents. In many cases, the cell contents of interest are the nucleic acids, i.e., the DNA or RNA. For example, cell lysis is typically performed on cells to release the DNA or RNA as the first step in amplification processes such as PCR.
Currently, cell lysing is most commonly accomplished chemically, such as by using detergents, solvents, or enzymes. However, this approach has the disadvantage of requiring a supply of the appropriate chemicals, with the associated storage and disposal problems.
Cell lysing can also be accomplished thermally. For example, the sample can be placed in thermal contact with a thermal block, such as a hot plate. However, such conventional heating techniques often take a relatively long time, which can result in excessive evaporation of the sample.
Microwave irradiation can also be used for cell lysing. Notably, microwave cell lysing appears to be related to thermal cell lysing. In particular, it has been found that the cell lysing accomplished by microwave irradiation can be attributed primarily to thermal effects. See Hiroshi Fujikawa, xe2x80x9cKinetics of Escherichia coli Destruction by Microwave Irradiation,xe2x80x9d Applied and Environmental Microbiology, March, 1992, p. 920-24. Thus, microwave irradiation stands as a particularly convenient method for heating samples to the extent required for cell lysing. In particular, samples can typically be heated for cell lysing more quickly using microwave irradiation than by conventional heating. This allows greater speed and efficiency in the cell lysing process. Additionally, the microwave cell lysing process is typically easier to control, because the microwave radiation may be easily turned on or off as required. Thus, the possibility of excessive evaporation of the sample is reduced.
However, the benefits of microwave cell lysis are more difficult to apply to small samples, i.e., samples less than one milliliter. Conventional microwave ovens apply microwave radiation at a frequency of 2.45 GHz. This frequency is used because of FCC regulations and because high power sources at this frequency are readily available. However, the heating of small samples at this frequency is not very efficient because the dimensions of the sample are small compared to the wavelength of the microwave radiation. This is a significant difficulty because in many cases, particularly when amplification techniques are to be used, only small samples are available.
Accordingly, there is a need to provide more efficient microwave cell lysis of small samples.
In a first principal aspect, the present invention provides a system for heating a sample. The system includes a microwave heating chamber having a wave-guide cavity with an input port and an output port and means for supporting the sample in the wave-guide cavity. A microwave source producing microwave radiation at a source power level at a source frequency is coupled to the input port so as to supply microwave radiation to the input port at an input power level. The source frequency is between 18 and 26 GHz. The microwave exits the output port at an output power level.
In a second principle aspect, the present invention provides a method for heating a sample. The sample is placed in a wave-guide cavity having an input port and an output port. Microwave radiation is applied to the input port of the wave-guide cavity at an input power level at a predetermined frequency to heat the sample at a predetermined temperature for a predetermined time. The predetermined frequency is between 18 and 26 GHz. The microwave radiation exits said output port at an output power level.
In a third principal aspect, the present invention provides a method for microwave cell lysis. The sample, which includes cells, is placed in a wave-guide cavity having an input port and an output port. Microwave radiation is applied to the input port of the wave-guide cavity at an input power level at a predetermined frequency for a predetermined period of time, the predetermined period of time being sufficient for lysis of said cells. The predetermined frequency is between 18 and 26 GHz. The microwave radiation exits said output port at an output power level.
By using microwave radiation with a frequency in the range of 18 to 26 GHz the heating of small samples, and, thus, cell lysing, is much more efficient than when the conventional microwave frequency of 2.45 GHz is used.